Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope. It is being used in planetarium projectors. Just set your coordinates and go.

Stellarium key features:

Realistic simulation of the sky, sunrise and sunset

Default catalogue of over 600,000 stars

Downloadable additional catalogues for up to 210 million stars

Catalog data for all New General Catalogue (NGC) objects

Images of almost all Messier objects and the Milky Way

Artistic illustrations for all 88 modern constellations

More than a dozen different cultures with their constellations

Solar and lunar eclipse simulation

Photorealistic landscapes (more are available on the website)

Scripting support with ECMAScript (a few demo scripts are included)

Extendable with plug-ins: 8 plug-ins installed by default, including:

artificial satellites plug-in (updated from an on-line TLE database)

ocular simulation plug-in (shows how objects look like in a given ocular)

Solar System editor plug-in (imports comet and asteroid data from the MPC)